The need to generate uniform or homogeneous patterns of electron beams directed at suitable targets in order to minimize localized heating and concomitant target damage is well known to those skilled in the art of particle accelerator, laser processing and the like operations. Such requirements also exist in such industrial applications as ion implantation and in medical therapy using charged particle beams. Commonly, sinusoidal or rotating beam raster systems are used to produce beam patterns that constantly vary the area of the target that is impacted by the beam with the objective of avoiding localized heating of the target material.
Beam rastering in a common practice for dealing with high local power deposition in accelerator and the like apparatus that involve beam interaction with a target. However, the rastering technique is limited because it is not always possible to increase the area covered by the rastered beam at the target face fast enough to be able to dissipate all of the generated heat. Also, large beam rastering can be a source of systematic errors in many experiments and cause elevated experimental and environmental radiation background, especially in experiments involving electron beams.
Another common practice in such circumstances is making the target moveable, and designed large enough to be able to dissipate all of the power deposited thereon. The position of the impact area in the target changes in time in essentially the same way as occurs in the rastering method. The advantages of such a method include a much larger capability to dissipate locally deposited heat, and the option to keep the position of the beam interaction region fixed in the laboratory frame. While such target movements sometimes are adequate to solve the target overheating problem they often do not provide adequate cooling of the target between beam impacts to adequately avoid target overheating. For example, target rotation with a constant beam direction, i.e. without rastering of the particle beam, can provide adequate cooling in some circumstances where target speed can be slowed adequately. This, however, is not an ideal solution nor is it appropriate for many of the situations in which particle, laser or the like beams are applied. This is especially true in those case where beam impact is necessary for a prolonged period of time to obtain a desired experimental result.
Target cooling in such applications is further complicated by the general location of particle beam, laser or the like targets in, for example, vacuum environments that do not permit the easy use of convection or conductive cooling techniques. Such is particularly true in those cases where localized target overheating is sought to be avoided by target rotation.
Thus, there exists a need for an apparatus and method that permits adequate target movement and/or cooling during particle or the like beam impact to provide the level of target cooling necessary to obtain satisfactory target/beam interaction without overheating.